Isolation and structure determination of natural products exhibiting pronounced physiological activity are being carried out. A large proportion of the work is carried out in cooperation with entomologists, biochemists and plant physiologists, the emphasis being placed on potent natural products which are present in microquantities and noncrystalline. Absolute configurations of the moulting hormones and juvenile hormones, and structural elucidation of complex fluorescent minor bases in various tRNA Phe are some results achieved so far.